Contributor: Gordon K. Klintworth
GM1-gangliosidosis type III (adult-onset GM1-gangliosidosis, chronic GM1-gangliosidosis, OMIM # 230650) is a subtype of  GM1-gangliosidosis and it is allelic with GM1-gangliosidosis type I and GM1-gangliosidosis type II and is caused by mutations in GLB1. The condition becomes manifest in adulthood and has a chronic course characterized by mental deterioration, myoclonic epilepsy, ataxia, and angiokeratomas. Clinical signs include gait disturbance, dysarthria, and a slowly progressive dystonia affecting the face and limbs. There is little intellectual or visual impairment. This type of  GM1-gangliosidosis has been recognized as a clinical entity only during recent years owing to an increased number of cases diagnosed in adult neurology clinics.